diff --git a/lib/gssapi/Makefile.am b/lib/gssapi/Makefile.am
index 4e08298c3..df3b5eb7c 100644
--- a/lib/gssapi/Makefile.am
+++ b/lib/gssapi/Makefile.am
@@ -9,6 +9,7 @@ AM_CPPFLAGS += \
 	-I$(srcdir) \
 	-I$(srcdir)/gssapi \
 	-I$(srcdir)/mech \
+	-I$(srcdir)/ntlm \
 	-I$(srcdir)/krb5 \
 	-I$(srcdir)/spnego \
 	$(INCLUDE_libintl) \